The present invention relates to a floppy disk drive (FDD) for an information processing device, etc., and more particularly to a circuit for adjusting the index of a medium for the FDD.
FIGS. 5A to 5C are plan views showing the conventional 8-inch, 5.25-inch and 3.5-inch floppy disk drive (hereinafter referred to as FDD as necessity requires), respectively. As seen from FIGS. 5A and 5B, each medium of the 8-inch FDD 1 and the 5-inch FDD 1 is provided with an index hole la which serves to detect one index pulse produced whenever the FDD 1 makes one revolution, thereby determining the start point of the rotating FDD 1. The index pulse is produced in such a manner that the index hole la is optically detected through a hole made in a jacket or cartridge to be converted into an electrical signal.
On the other hand, the medium of the 3.5-inch FDD as shown in FIG. 5C has no index hole. In order to detect the index therefor in terms of an index pulse, a reflection plate is attached in the outer periphery of a rotor and a reflective photo-interrupter is also provided so as to be opposite to the reflection plate; the rotor is integrally formed with a spindle motor of a chucking mechanism for clamping the FDD. When the reflection plate is opposite to the photo-interrupter due to one revolution of the rotor, the above index pulse is produced each revolution of the FDD.
The index pulse will be used to indicate a reference position from which data read or write for the medium is started.
FIG. 6 is a sectional view of the medium chucking mechanism for clamping the above 3.5-inch FDD with no index hole. As seen from FIG. 6, a medium composed of a metallic hub 2 and a disk 3 is fixed to a spindle motor composed of a rotor 6 and a driving coil 7 by means of a spindle hub including a chucking magnet 4 and a driving pin 5.
An explanation will be given of a procedure of chucking the FDD with reference to FIGS. 7A to 7C. FIG. 7A is a plan view when the FDD 1 is mounted on the chucking mechanism. FIG. 7B is a plan view when positioning the FDD 1 is started. FIG. 7C is a plan view when positioning the FDD is completed.
First, as seen from FIG. 7A, the metallic hub 2 for the FDD 1 is adsorbed onto the chucking magnet 4 of the spindle and a spindle shaft 10 is inserted into a chucking hole 8. Next, as seen from FIG. 7B, the driving pin 5 enters a positioning hole 9 of the medium. Finally, as seen from FIG. 7C, the position of the medium is accurately fixed by the spindle shaft 10 and the driving pin 5. Thus, positioning of the FDD has been completed.
It should be noted that the positional relationship between the driving pin 5 and the reflecting plate of the spindle motor is fixed so that the position of starting read or write for the medium and that of the reflection plate when the FDD 1 has been clamped in its chucking mechanism are also fixed. However, the position of the reflection place when assembling the spindle motor may deviate slightly.
Meanwhile, in some FDD control devices, data read is inhibited during a certain period immediately after the index pulse has been produced. Therefore, in FDD's when using such a FDD control circuit, in many cases, relative positions of the indices for these FDD's are made coincident.
In order to remove the above positional deviation, the index adjustment circuit as shown in FIG. 8 has been conventionally used. The index adjustment circuit of FIG. is composed of an index sensor 11, a timer circuit 12 comprising a resistor, a variable resistor, a capacitor, etc. and a control circuit 13.
In operation, an input index waveform from the index sensor 11 is delayed by the timer 12, and its read/write timing is taken by the control circuit 13.
Thus, the conventional circuit arrangement can adjust the index waveform by changing values of the resistor and the capacitor.
However, since the conventional index adjustment device for the FDD user the capacitor and the resistor and the variable resistor the value of which is to be adjusted using the robot provided in the timer circuit, its reliability may be influenced by ambient conditions of temperature, used voltage, shock, etc.